Transition metal carbides are generally known to show a unique combination of solid-state properties including exceptional mechanical hardness, excellent electrical and thermal conductivity, and very high melting points in addition to being chemically inert and wear resistant (see Encyclopedia of Inorganic Chemistry, Volume 1, pp. 519–531, 1994). Use of transition metal carbides has been suggested for several different types of film application, including wear-resistant coatings, hard coatings, and diffusion barrier films.
Atomic Layer Deposition (ALD), or, as it is often called, Atomic Layer Epitaxy (ALE), is a method of manufacturing thin films that was first investigated in the 1970s. ALD refers to a process of depositing a thin film onto a substrate that involves sequential and alternating self-saturating surface reactions. As compared to other thin film deposition methods, such as Physical Vapor Deposition (PVD) (e.g., evaporation or sputtering), Chemical Vapor Deposition (CVD), or Metal Organic CVD (MOCVD), ALD offers several benefits. These benefits and the principles of ALD are well known to those skilled in the art (Atomic Layer Epitaxy, Suntola, T. and Simpson, M., eds., Blackie and Son Ltd., Glasgow, 1990). Although ALD has been used in connection with many materials, it has not been successfully used for transition metal carbides.
One attempt to process films with transition metal nitrides using ALD is described by Leskelä and Niinistö in Atomic Layer Epitaxy. Id. at 18–21. Leskelä and Niinistö prepared niobium nitride (NbN) films for niobium-based superconductors using metal chlorides and ammonia. As stated on page 19, “[t]he interest in niobium nitride films stems from its superconductivity below 17K.” Because “the properties of nitrides can be in some cases improved by the addition of carbon,” Leskelä and Niinistö also used ALD to add carbon to NbN films. Id. at page 20. Specifically, they used methane as the carbon source, postulating that the carbon would enhance the mechanical and superconductivity properties of the NbN films. “A black niobium carbide (NbC) film was formed but the growth rate was slow and the film was amorphous.” Id. at 21.
Another attempt to process transition metal nitride films by ALD is described in Marika Juppo's academic dissertation entitled Atomic Layer Deposition of Metal and Transition Metal Nitride Thin Films and In Situ Mass Spectrometry Studies (Helsinki University, pp. 48–49, 2001). Juppo describes a method of depositing transition metal nitrides using titanium tetrachloride (TiCl4), trimethylaluminum (Al(CH3)3), and ammonia (NH3) that produces titanium aluminum nitride (Ti(Al)N) films having some carbon content. Persons of ordinary skill in the art know that a nitrogen-deficient transition metal carbide film (i.e., containing less than 10 atomic-% nitrogen) cannot be formed using this method or any similar method for growing nitrides.
U.S. Patent Application Publication No. 2002/0086504 of Park et al. describes a process of manufacturing a semiconductor device having a metal gate electrode formed by depositing a (TixAly)1−zNz film over a gate insulating film. The process implements CVD or ALD for depositing the (TixAly)1−zNz film and for controlling a work function of the film.
U.S. Pat. No. 6,482,262 (the “'262 patent”) to Elers et al. describes an attempt to process transition metal carbide films by ALD. The '262 patent describes a method of depositing transition metal carbide thin films by ALD “in which a transition metal source compound and a carbon source compound are alternatively provided to the substrate.” Abstract. The '262 patent describes the use of several carbon-containing compounds as the carbon source compound, including a boron compound comprising at least one boron atom and at least one carbon atom, a silicon compound comprising at least one silicon atom and at least one carbon atom, and a phosphorus compound comprising at least one phosphorus atom and at least one carbon atom. Due to the chosen carbon sources, the carbide films of the '262 patent are likely to contain trace amounts of boron, silicon, or phosphorus contamination. Because deposition occurs at high temperatures, the substrate surface layers may be affected by the contaminated carbide film or by boron-, silicon-, or phosphorus-containing carbon source compound in contact with the substrate, which can negatively affect the operability of devices made with the resulting films. The '262 patent also describes using a hydrocarbon as the carbon source, but states that this alternative carbon source is undesirable because its use involves activation of the reaction with a plasma, requiring a more complicated and expensive reactor design.
Another attempt to process metal films by ALD is described in U.S. Pat. No. 6,174,809 (the “'809 patent”) to Kang et al. The '809 patent describes a method of forming metal layers using ALD in combination with a sacrificial metal layer first formed on a semiconductor substrate and subsequently reacted with a metal halide gas to form the desired metal layer. For example, a pure aluminum sacrificial metal layer is formed by the deposition of trimethylaluminum (Al(CH3)3) (hereinafter “TMA”) reduced by hydrogen that is reacted with titanium tetrachloride (TiCl4) to convert the aluminum sacrificial metal layer into a titanium metal layer. Any carbide formation is naturally suppressed by the use of a reducing hydrogen. Consequently, transition metal carbide films cannot be formed using this method for growing metals.
U.S. Publication No. 2003/0022457 A1 to Gutsche et al. describes a method of forming a metal carbide layer involving depositing an alternating sequences of metal-containing layers and carbon-containing layers. The resulting layered structure is then heated in a separate step in a separate tool (such as a rapid thermal process) to migrate the carbon-containing and metal-containing layers together and form a metal carbide layer. However, this high temperature treatment decreases the capacity of the process steps and requires the use of expensive and complex manufacturing equipment.
The present inventors have recognized a need for methods of depositing onto a substrate a transition metal carbide film exhibiting chemical inertness and electrical conductivity, as well as methods preferably offering the user the ability to tailor and fine-tune the deposition process and film properties while exhibiting good processibility and reasonable growth rate.
The present inventors have also recognized a need for transition metal carbide thin films that can be easily implemented in advanced semiconductor structures and that include minimal impurities that would interact with neighboring layers and thereby negatively affect operation of the semiconductor structure.